Can't find my WordPress username

I'm trying to slurp my blog to a book via Booksmart. It requires me to enter my wordpress.com username and password.

Funny thing is, I've been blogging forever without having a username and password. A friend set my blog up, and for me to sign in to my blog's back end, I just type in the domain name, followed by /wp-admin. The full address is http://www.romneyexperience.com/wp-admin . There, I sign in, but just with a username for my specific blog, and a password. That username doesn't work for signing in to wordpress.com.

So now I've got a username on wordpress.com that I've signed up for separately, but I have no idea how to link my blog to this new account. Again, my need to do this is to tell the Booksmart program what my username and password are, so it can sign in and find my blog. Please help if you have any thoughts.